Bar code scanning system with offset optical axes

ABSTRACT

A scan module and an optical system such as for a bar code scanner wherein the optical system has an axis of outgoing (illumination) light offset from the axis of collected light, arranged to limit the dynamic range of the collected light and thus the dynami9c range within which the bar code scanner detector and signal processor must function. Preferably, the outgoing axis and the collection lens axis are substantially parallel.

[0001] This application is a continuation of application Ser. No.09/575,695 filed Jul. 6, 2000 which is a divisional of application Ser.No. 08/942,399 filed Oct. 1, 1997 U.S. Pat. No. 6,166,375 which claimspriority to provisional application Ser. No. 60/027,963 filed Oct. 8,1996, each of which is incorporated by reference.

BACKGROUND

[0002] The field of the present invention relates generally to datacapture systems and more specifically to data readers, such as scannersand bar code reading devices.

[0003] Although the following description of this invention makesreference to bar code scanners, by way of example, the invention itselfis equally applicable to other methods and systems for data reading andforms of encoded data (indicia) other than bar codes.

[0004] From an operational point of view, bar code scanners aretypically operated in one of two modes, fixed or handheld. In the fixedmode of operation, objects with bar codes thereon are moved to or past astationary bar code scanner for scanning. In the handheld mode ofoperation, a portable bar code scanner is typically oriented and/ormoved to the bar code label to be read. For purposes of thisdescription, the term bar code scanner shall henceforth denote a scannerof the spot scanning type, wherein an illumination spot is moved acrossa bar code. The bar code scanners described herein may utilize anynumber of scan patterns comprising any number of scan lines in anyconfiguration suitable for bar code scanning applications and projectedthrough any number of scan windows. Further details regarding scanlines, scan patterns, and scan windows may be found in U.S. applicationSer. Nos. 60/010,935 and 08/792,829 entitled “Multi-Aperture Data Readerfor Multi-Mode Operation” and Ser. No. 60/021,783 and U.S. Pat. No.5,962,838 entitled “Bar Code Scanner with a Manually Switchable ScanPattern” herein incorporated by reference as if fully set forth herein.

[0005] A bar code label comprises a series of parallel dark bars ofvarying widths with intervening light spaces, also of varying widths.The information encoded in the bar code is represented by the specificsequence of bar and space widths, the precise nature of thisrepresentation depending on the particular bar code symbology used.Methods for reading bar codes may comprise generation of an electronicsignal wherein a signal voltage alternates between two preset voltagelevels, one representing a dark bar and the other representing a lightspace. The temporal widths of these alternating pulses of high and lowvoltage levels correspond to the spatial widths of the bars and spaces.It is this temporal sequence of alternating voltage pulses of varyingwidths which is presented to an electronic decoding apparatus fordecoding.

[0006] A common and well-developed method for converting the spatialbar/space sequence into a temporal high/low voltage sequence is themethod of bar code reading. A bar code scanner typically has an opticalsystem (also referred to as an opto-mechanical system) with twosubsystems: an illumination subsystem which produces an illuminationbeam and a collection subsystem which collects and detects light. Theillumination subsystem, typically comprising a light source, a focusinglens, and a scan engine, focuses an outgoing light beam to a minimumdiameter, known as the waist, and generates a scan pattern so that theillumination beam, or spot, is likely to be scanned across a bar code.The collection subsystem, which typically includes a collection lens, oralternatively a concave collection mirror or functional equivalentthereof, and a photodetector, collects at least some of the lightscattered and/or reflected from the bar code illuminated by theillumination beam and focuses the same onto the detector. Thephotodetector produces an analog signal having an amplitude determinedby the intensity of the collected light. The photodetector, for example,may generate a high voltage when a large amount of light scattered fromthe bar code impinges on the detector, as from a light space, andlikewise may produce a low voltage when a small amount of lightscattered from the bar code impinges on the photodetector, as from adark bar. When the illumination and collection paths/axes aresubstantially coincidental, the system is typically referred to as aretro-directive.

[0007] The illumination source in “spot” bar code scanners is typicallya laser, but may comprise a coherent light source (such as a laser orlaser diode) or a non-coherent light source (such as a light emittingdiode). A laser illumination source offers the advantages of highintensity illumination which may allow bar codes to be read over a largerange of distances from the bar code scanner and under a wide range ofbackground illumination conditions (the area in which a bar code may beconsistently read by the scanning system is commonly referred to as thedepth of field). The scanner's ability to read bar codes at the outerextremes of the depth of field (far field) is, however, limited in partby collected optical power, which decreases approximately as the inverseof the square of the distance from the scanner. It is desirable for abar code scanner to be capable of reading bar codes over an extendeddistance from the scanner, that is, to have a large depth of field. Manyimprovements have been made to bar code scanners to extend their depthof field. One such improvement is disclosed in Rudeen et al. U.S. Pat.No. 5,479,011 entitled “Variable Focus Optical System For Data Reading”,the patent being hereby incorporated by reference. The Rudeen '011patent discloses a variable width aperture disposed in the outgoingoptical path thereby varying the location of the beam waist and enablingthe scanner to read bar codes over a greater depth of field. Anotherembodiment is disclosed in Bailey et al. U.S. Pat. No. 4,978,860entitled “Optical System for a Large Depth of Field Bar Code Scanner”,the patent being hereby incorporated by reference. The Bailey '860patent discloses a scanner utilizing a tilted detector array to extendthe depth of field of the reading device. Another improvement isdisclosed in Reddersen et al. U.S. Pat. No. 5,438,187 entitled “MultipleFocus Optical System for Data Reading Applications” the patent beinghereby incorporated by reference. The Reddersen '187 patent discloses asystem which utilizes a multiple focus lens as a means of extending thebar code scanner's depth of field.

[0008] There have been several other suggestions on how to increase thedepth of field in previous bar code scanner systems. In another system,a focusing lens is designed with an axially movable lens element (suchas a zoom lens) to permit changing the focusing power to change thedepth of field. Such systems require complicated mechanical lensadjustment and/or may require the user to manually make focusingadjustments. It is desirable to eliminate the need for focus adjustmentsby the user or complicated mechanical devices.

[0009] Another previous method employed to improve depth of field forbar code scanning systems is over-filling the detector in the nearfield. Because collected optical power decreases approximately as thesquare of the distance from the scanner, many bar code scanning systemsamplify the detected signal in order to read bar codes in the far field.Amplification boosts the detected signal generated by the photodetector.This amplification (or gain), however, boosts some detected signals,typically in the near field, to levels beyond the dynamic range of thebar code scanner's detection and signal processing systems. Althoughenabling a bar code scanner to read bar codes in the far field,amplification of detected signals generated from scanning bar codes inthe near field will frequently boost the detected signal to levelsoutside the functioning dynamic range of the detection and signalprocessing systems. Increasing the dynamic range of the detection andsignal processing systems (components) typically requires more expensiveand complex components with a potential concomitant deterioration of barcode scanner performance. That is, a lower first pass read rate of thebar code scanner and/or a higher mis-read rate. To improve the depth offield and first pass read rate of such systems, previous collectionsubsystems are designed to over-fill the detector in the near field.That is, the collection lens, or alternatively the collection mirror orfunctional equivalents thereof, is designed so the collected light inthe near field focuses a spot at the center of the detector which islarger than the detector, thereby over-filling the detector. All thecollected light is not detected, thereby limiting the dynamic range ofthe detected and processed signal. Many other secondary factors mayimpact the dynamic range, but it is nonetheless desirable to limit suchimpact. FIG. 7 is a plot of the power collected vs. the distance fromthe collection lens for a certain bar code scanning system andparticular conditions wherein the detector is filled when the bar codeis approximately 5.3 inches from the detector. As indicated in FIG. 7,the dynamic range is limited from approximately 800 nW to 2000 nW when abar code is scanned in a range of approximately 4-8.5 inches from thecollection lens. Consequently, bar codes over a greater depth of fieldmay be read for a given dynamic range of detection and signal processingsystems.

[0010] Other previous bar code scanning systems have had optical systemswhich offset the collection axis from the axis of outgoing light,however, significant differences and purposes exist in these previoussystems. These optical systems were designed with an offset to minimizethe amount of collected light the illumination focusing lens was keepingfrom reaching the detector while substantially coaxially aligning thecollection axis and the axis of outgoing light in retro-directive barcode scanning systems. Initially the two axes were very close together(approximately 0.1 inches apart) because the focusing lens wassuperimposed (off the central axis of the collection lens) in thecollection lens.

[0011] Moreover, the collection lens and focusing lens were aligned suchthat their optical axes optimally converged within the scan volume (wereas close together as possible).

SUMMARY OF INVENTION

[0012] The present invention is directed to a method of data reading andan optical system such as for a bar code scanner. In a preferredconfiguration, the optical system has an axis of outgoing (illumination)light offset from the axis of collected light, which limits the dynamicrange of the collected light and therefore the dynamic range withinwhich the bar code scanner detector and signal processor must function.Preferably, the outgoing axis and the collection axis are substantiallyparallel.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is a schematic diagram of an illumination subsystem and acollection subsystem according to a preferred embodiment of the presentinvention.

[0014] FIGS. 2-6 depict the size and location of the collected andfocused spot on the detector.

[0015]FIG. 7 is a graph of collected power versus distance for anoptical system which over-fills the detector in the near field.

[0016]FIG. 8 is a graph of collected power versus distance for an offsetoptical system.

[0017]FIG. 9 is a side perspective view of a scanner module with anoutgoing optical axis offset from the axis of the collection optics.

[0018]FIG. 10 is a cross sectional view of the scan module of FIG. 9taken along line 10-10.

[0019] FIGS. 11 is a side perspective view of the scan module of FIG. 9with the printed circuit board removed to reveal internal components.

[0020]FIG. 12 is a front side perspective view of the scan module ofFIG. 9 with the printed circuit board removed to reveal internalcomponents.

[0021]FIG. 13 is a top view of the scan module of FIG. 9 with theprinted circuit board removed to reveal internal components.

[0022]FIG. 14 is a bottom side assembly drawing of the printed circuitboard of the scan module of FIG. 9.

[0023]FIG. 15 is a top side assembly drawing of the printed circuitboard of the scan module of FIG. 9.

[0024]FIG. 16 is a cross sectional view of an alternate scan moduleconfiguration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Preferred and alternative embodiments of the subject inventionwill now be described in detail with reference to the drawings.

[0026] In a preferred configuration as shown in FIG. 1, the opticalsystem is provided with an axis 115 of outgoing (illumination) lightoffset from and substantially parallel to the axis 135 of collectedlight to limit the dynamic range. Offsetting the two axes will cause thespot generated by the collection lens 130 to migrate across the detector140 (or array of detectors) when bar codes 150 are read in the nearfield. Migration limits the dynamic range required of the detection andsignal processing systems because as the bar code moves closer to thecollection lens, less of the light collected therefrom impinges on thedetector 140 when the bar code 150 is scanned. Moreover, signalamplification may be increased without exceeding the dynamic range ofthe detection and signal processing systems, which enables the bar codescanner 10 to more readily and reliably read bar codes in the far field.The depth of field is thereby extended such that the volume within whicha bar code may be successfully scanned (i.e., scan volume) is larger,which, of course, increases the likelihood a bar code will be readduring its first pass (when swept by or presented to the scanner).

[0027] Alternatively, signal amplification may be left unchanged therebyimproving the performance of the detection and signal processingsystems. The subject invention limits the dynamic range within which thedetection and signal processing systems must function. Detection andsignal processing components function optimally and bar code scanning isimproved (first pass read rate and reading accuracy) if these componentsare not pushed to their dynamic range limits. Alternatively, lessexpensive and/or complex components which are designed to work within asmaller dynamic range may be used without compromising bar code scannerperformance.

[0028] To offset the two axes, the focusing lens 110 may be locatedadjacent to the collection lens 130 but not superimposed thereon (sideby side). This arrangement keeps the focusing lens 110 from preventinglight from reaching the detector 140.

[0029] The outgoing axis 115 is preferably parallel to the collectionaxis 135, but may vary somewhat from absolutely parallel. In an actualconstruction the alignment of the axes 115, 135 varies by about 3°. Thusthe alignment may vary from substantially parallel (about +/−5°) or mayvary by even a greater amount (e.g. 10°) depending upon the particularconfiguration.

[0030]FIG. 1 illustrates an optical system 10 comprising light source100 (typically a visible laser diode), focusing optics 110 (preferablyboth light source 100 and necessary focusing optics are housed in avisible laser diode module), scanning mechanism downstream of focusingoptics 110 aligned on outgoing optical axis 115, detector 140(preferably a photodiode), and collection optics 130 aligned oncollection optical axis 135, and an imaging photodetector 140 at focalplane 120. The scan generating mechanism is not shown, but is well knownand may comprise any suitable scanning mechanism such as a pivotingmirror, rotating mirror, rotating hologram, or moving light source. Anobject 150 to be scanned with a bar code affixed thereto or printedthereon is shown at focal plane 120. The offset of the two axes 115 and135, as measured by distance D3, causes the spot focused on detector 140by collection lens 130 to migrate across detector 140, and eventuallyoff detector 140, as the object 150 is moved progressively closer tocollection lens 130 and is scanned. FIGS. 2-6 depict this migration.Other dimensions which figure prominently are D2, the distance fromdetector 140 to collection lens 130, and D1, the distance fromcollection lens 130 to the bar code to be scanned. In a preferredembodiment of the subject invention D1 is approximately 15 inches, D2 isapproximately 0.6 inches, D3 is approximately 3 inches, and focal lengthof collection lens 130 is approximately 0.6 inches, and the axis 115 issubstantially parallel to axis 135 (varying by about 3°). FIGS. 2-6illustrate the location of the spot 105 at decreasing distance D asmeasured from the bar code scanner nose (not shown) to the scanned barcode, wherein the distance from the collection lens 130 to the nose isapproximately 3 inches: </paragraph>

[0031] FIG. D—Distance from scanner nose to barcode

[0032]FIG. 2 270 mm

[0033]FIG. 3 170 mm

[0034]FIG. 4 70 mm

[0035]FIG. 5 20 mm

[0036]FIG. 6 0 mm

[0037] As illustrated in FIGS. 2-6 not only does the center of the spot105 focused on detector 140 migrate farther from the center of thedetector as the bar code gets progressively closer to collection lens130 (near field), but defocusing occurs, that is, the spot size growslarger. As the bar code scanned gets progressively closer to collectionlens 130, the intensity of the light collected also increases as theinverse square of the distance from collection lens 130. Therefore, asgraphically depicted in FIG. 8, the dynamic range is limited as a resultof a portion of the spot incident on detector 140 having migrated offthe detector 140.

[0038] Thus the optical system 10 provides an improved means of limitingthe dynamic range. As shown by a comparison of the graphs of FIG. 7 andFIG. 8, moving the collected spot off the detector (FIG. 8) lowers thepower collected more gradually than simply over-filling the detector(FIG. 7). Although a number of factors may impact these plots, migratingthe incident spot off the detector has the advantage of limiting thedynamic range over a greater depth of field. Offsetting outgoing opticalaxis 115 from collected optical axis 135 limits the dynamic range to agreater degree than simply over-filling the detector.

[0039] Limiting the dynamic range has a number of benefits. Collectedsignal amplification may be increased without exceeding the dynamicrange of the detection and signal processing systems when bar codes arescanned in the near field. Amplification enables the bar code scanner toread bar codes in the far field thereby extending the depth of field andincreasing the likelihood a bar code will be read during its first sweepby or presentation to the scanner. Other factors play a role in a barcode scanner's ability to extend its depth of field by signalamplification, including the bandwidth of the amplification system, spotsize in the far field, and the signal to noise ratio. Nonetheless, manysystems which offset the axis of outgoing light from the axis ofcollected light will be able to increase the amplification of thedetected signal which will enable the bar code scanner to read bar codesfarther from the scanner without compromising performance in the nearfield (i.e., extend the depth of field). An increase in the size of thedepth of field increases the scan volume within which a bar code may beread, which in turn increases the likelihood that a bar code presentedto or swept by the bar code scanner will be in the scan volume and thusbe successfully read. First pass read rate is a critical performancecriterion for bar code scanners.

[0040] On the other hand narrowing the dynamic range of a bar codescanning system while maintaining the depth of field may also be ofbenefit. Detection and signal processing systems are able tosuccessfully read bar codes within a certain range of collected signals.In lieu of increasing amplification as a means of extending the depth offield when the subject invention is employed, alternativelyamplification may remain the same so that the detection and signalprocessing systems experience a more limited dynamic range, that is, asmaller dynamic range. Detection and signal processing performancedeteriorates at the extremes of their dynamic range. Limiting thedynamic range within which the detection and signal processing systemstypically have to operate improves detection and signal processingperformance which in turn improves bar code scanner performance(including edge detection, first pass read rate, and scanning accuracy).Alternatively, less expensive and/or complex components which aredesigned to work within a smaller dynamic range may be used withoutcompromising bar code scanner performance.

[0041] As depicted in FIG. 1, wherein collection lens 130 and focusinglens 110 are side by side and not superimposed, focusing lens 110 doesnot prevent backscattered or reflected light from the scanned bar codefrom reaching the detector 140. This arrangement allows the maximumlight possible, for a given collection system, to be collected. Althoughthis may be undesirable when bar codes are scanned in the near field, itis critical to bar code scanner performance in the far field and toextending the depth of field.

[0042] The various optical systems described above may be provided inefficient configurations incorporated into a scan module. FIGS. 9-13illustrate one such scan module 400 incorporating the optical system ofFIG. 1. The scan module 400 includes (1) a main housing 450, (2) adithering assembly 401, (3) a laser diode module 452 and a collectionlens 470 mounted to the housing 450 via clamp 454, (4) a collection foldmirror 472 positioned at 45° behind the collection mirror, and (5) adetector 419 mounted to the underside of PCB 415 over collection foldmirror 472.

[0043] The collection lens 470 may be constructed from any suitable lensmaterial such as glass or plastic. The lens 470 is preferablyconstructed from plastic and integrally molded within its own plasticsupport bracket 471. The bracket 471 is readily assembled by sliding thebracket 471 into place within the housing 450. The bracket 471 includesa U-shaped end portion 471 a which securely attaches to a lip 451 in aside of the housing 450. This integral collection lens 470 and lensbracket 471 assembly reduces the number of module components therebysimplifying module structure and assembly.

[0044] The dithering assembly 401 comprises a dithering mirror 402mounted to mirror bracket 403. A mounting member 414 mounted on a baseor housing member 450, bending member or flexure 412 is mounted betweenthe mounting member 414 and the mirror bracket 403. The mounting bracket403 is pivotally supported on the mounting member 414 via bending member412. Though they provide no function during normal operation, shockpin(s) 413 are included to constrain motion of the ditherer under highexternal mechanical conditions (such as when the unit is dropped) toprevent damage to the bending member 412. The drive magnet 404 is alsomounted on the mirror bracket 403 with the drive coil 406 mounted to thePCB 415. The feedback sensor 408 (such as a Hall effect sensor) ismounted to the underside of the PCB 415 (shown by the dashed lines inFIG. 9) in a position adjacent the feedback magnet 410 mounted to themirror bracket 403. The motion of mirror 402 is driven by passing anoscillating drive current through drive coil 406. The drive coil 406(shown by the dashed lines in FIG. 9) is attached to the underside ofPCB 415, the actuator coil leads 407 of the drive coil 406 extendingthrough the board 415. When the PCB 415 is installed, the drive coil 406is positioned in the recess 405 adjacent the actuator magnet 404. Travelstops 416, 416 are positioned to restrict the amplitude of the ditheringmotion to a maximum dithering amplitude.

[0045] In operation, the laser diode module 452 generates a laser beam460 which is focused by a collimating lens located within the modulebarrel, passed through the exit slot, and directed onto the ditheringmirror 402. The laser diode module 452 is positioned adjacent to thecollection lens 470. The collection lens 470 has a cutout notch 473 onone side within which the diode module 452 is positioned therebyproviding further compactness of structure and enabling the diode 452 tobe located closer to being coaxial with the collection lens 470. Thedithering mirror 402 oscillates to produce a scan line. Return signalreflected and/or scattered off an object (e.g. the bar code symbol on anitem being scanned) returns to the dithering mirror 402 and is directedto collection mirror 470 which focuses the return beam which isreflected by 45° fold mirror 472 up to the detector 419 (such as aphotodiode). The detector 419 detects and converts the signal intoelectrical impulses corresponding to, in the case of reading a barcodesymbol, the bars and spaces.

[0046] The system may comprise additional laser beam focusing featuressuch as described in U.S. Pat. Nos. 5,565,668 and 5,641,958 hereinincorporated by reference.

[0047] The dithering mirror 402 may be a flat mirror as shown oralternately may be curved thereby providing focusing power. The mirror402 may alternately include a small inset mirror attached to or moldedwith the mirror 402 for reflecting the outgoing beam 460.

[0048] The scanner PCB 415 is also configured to provide for compactconstruction. FIG. 14 is a bottom side assembly drawing of the printedcircuit board 415 of the scan module 400 of FIG. 9. Several scannercomponents are efficiently mounted on the underside of PCB 415 includingthe detector 419, the actuator coil 406 and the Hall sensor 408. Theonly electronic component not mounted to the PCB 415 is the laser diodemodule 452. The leads 453 of the diode module 452 are connected to theconnectors 456 on the PCB 415 by a ribbon cable (not shown). The ribboncable exerts minimal forces on the diode module 452 minimizing potentialfor misalignment.

[0049]FIG. 15 is an assembly drawing of the top side of the PCB 415illustrating that the top side of the board contains additionalelectronic components. By mounting components on both sides of theboard, the size of the printed circuit board may be minimized with allmodule electronics mounted on a single board. Further description of thePCB 415 and the dithering assembly 401 is contained in James E. Colleyet al. “DITHERING ASSEMBLIES FOR BARCODE SCANNERS” filed Sep. 19, 1997U.S. application Ser. No. 08/934,487 U.S. Pat. No. 6,152,372 hereinincorporated by reference.

[0050]FIG. 16 is a cross section of an alternate scan module with a viewsimilar to the cross section of FIG. 10, wherein the diode module 452′is mounted to the PCB 415 enabling all the electronic components of thescan module 400 to be compactly and efficiently assembled on a singleprinted circuit board. By locating the diode module 452′ either on thePCB 415 or adjacent thereto, it may be possible to connect the leads(not shown) of the diode 452′ directly to the PCB 415 eliminating theneed for the ribbon cable of the previous configuration.

[0051] In the scan module 400 of FIGS. 9-13, the axis 460 of theoutgoing beam and the axis 470 a of the collection lens 470 are offsetby an amount D3 (as defined in the schematic of FIG. 1). The D3 offsetin module 400 is about 0.25 inches. The offset amount for D3 is selectedto provide the desired degree of beam movement to correspond to desiredlimiting of dynamic range. Referring to FIGS. 2-6 and 8, the smaller D3,the less spot movement as the item is moved closer to the scanner. Asshown in FIG. 8, as the amount D3 approaches zero, that is as the twoaxes 115, 135 of FIG. 1 approach coaxial, the power on detectorapproaches the dashed line. The larger D3, the more spot movement andthe more rapidly the power on detector, designated by the solid line,drops off. If D3 becomes too large, then the spot may fall entirely offthe detector at near field and the power on detector would fall to zero.Thus, by experimentation for a particular scanner configuration, D3 maybe empirically chosen to provide the desired limiting of dynamic range.

[0052] In an alternate embodiment, means may be provided to adjust theoffset D3 thereby providing adjustable limiting of dynamic range. Suchmeans for adjusting the offset D3 may comprise, for example, suitablemechanical mechanisms which adjust the position of the beam axis 115,the source 100, the lens 110 or the lens 130. Alternately, the offset D3may be adjusted electro-optically such as via multiple beam sources,electrically controlled LCD element(s), or piezoelectric element(s).

[0053] A band pass filter, corresponding to the wavelength of theoptical beam, may be provided in the collection path to prevent light ofunwanted wavelength from reaching. The filter (not shown) may comprise asmall glass element attached directly to the detector 408 via doublesided tape or other suitable means and may be approximately the samesize as the detector.

[0054] Alternately, a corrective optical element, such a diffuser plate,may be disposed between the collection lens 470 and the detector 408such as described in application Robert W. Rudeen et al. Ser. No.60/054,962 entitled COLLECTION SYSTEM FOR RANGE ENHANCEMENT filed Aug.7, 1997 hereby incorporated by reference. The corrective optical elementmay provide further range enhancement. The corrective optical elementmay be conveniently attached directly to the detector 408 or to the bandpass filter described above thereby minimizing size and cost ofmanufacture. The corrective optical element and the band pass filter maycomprise: a single combined optical element; two separate opticalelements mounted together or separately.

[0055] Certain aspects of the preferred embodiments described above mayhave one or more of the following advantages:

[0056] to provide an optical system for a bar code scanner wherein areduced dynamic range is required of signal detection and processingsystems;

[0057] to provide an optical system for a bar code scanner which has alarger depth of field;

[0058] to provide an optical system for a bar code scanner whichimproves bar code scanning performance;

[0059] to provide an optical system for a bar code scanner wherein thedetection and signal processing systems may be simplified withoutcompromising bar code scanner performance;

[0060] to provide a simplified optical system producing a compact scanmodule without compromising bar code scanner performance;

[0061] to provide a scanning system or scan module with a simplifiedelectronic collection system without electronic gain control;

[0062] to provide a compact and efficiently constructed scan module;

[0063] to provide an optical system for a bar code scanner wherein thefocusing lens does not prevent backscattered or reflected light fromreaching the detector.

[0064] Though certain examples and advantages have been disclosed,further advantages and modifications may become obvious to one skilledin the art from the disclosures herein. The invention therefore is notto be limited except in the spirit of the claims that follow.

What is claimed is
 1. A method of data reading comprising the steps ofgenerating an optical beam and directing it along an outgoing axistoward an object to be read; collecting incoming light scattered and/orreflected from the object and focusing the incoming light along acollection axis into a spot on a detector; limiting dynamic range of theincoming light reaching the detector by offsetting the collection axisfrom the outgoing axis and causing the spot to migrate across andpartially off the detector when the object being read is located in anear field.
 2. A method according to claim 1 further comprisingincreasing the portion of the spot which falls off the detector as theobject is located nearer to the detector.
 3. A method according to claim1 further comprising decreasing the portion of the spot which falls onthe detector as the object is located nearer to the detector.
 4. Amethod according to claim 1 wherein the outgoing axis and the collectionaxis are arranged parallel.
 5. A method according to claim 1 wherein theoutgoing axis and the collection axis are arranged substantiallyparallel +/−5°.
 6. A method of data reading comprising the steps ofgenerating an optical beam and directing it along an outgoing axistoward an object to be read; scanning the optical beam with a scanningmechanism for producing at least one scan line toward the object;collecting incoming light scattered and/or reflected from the object viathe scanning mechanism to a collection lens and focusing the incominglight into a spot on a detector; offsetting the outgoing axis theoptical beam from an incoming axis of the collection lens.
 7. A methodaccording to claim 6 further comprising causing the spot to migrateacross and partially off the detector when the object being read islocated in a near field.
 8. A method according to claim 6 furthercomprising causing the spot to migrate on the detector such that as theobject being read is moved nearer the collection lens, an increasingportion of the spot falls off the detector.
 9. A method according toclaim 6 further comprising decreasing the portion of the spot whichfalls on the detector as the object is located nearer to the detector.10. A method according to claim 6 further comprising increasing theportion of the spot which falls off the detector as the object islocated nearer to the detector.
 11. A method according to claim 6wherein the outgoing axis and the collection axis ar e arranged parallelto each other.
 12. A method according to claim 6 wherein the outgoingaxis and the collection axis are arranged substantially parallel +/−5°to each other.
 13. A optical scanning system comprising a light sourcefor generating an optical beam along an outgoing optical path toward anobject to be scanned; a detector for detecting light reflected off theobject; a one-piece plastic molded lens assembly including a collectionlens portion and a bracket portion, the bracket portion being mounted inthe housing and the collection lens portion collecting the lightreflected and/or refracted off the object and focusing it onto thedetector; a scanning mirror assembly disposed in the outgoing opticalpath for scanning the optical beam for producing at least one scan linetoward the object and for reflecting light reflected and/or refractedoff the object toward the collection lens portion.
 14. A scanning systemaccording to claim 13 wherein the collection lens comprises a notch inone side thereof, and wherein the light source comprises a laser diodemodule disposed in the notch.
 15. A scanning system according to claim13 wherein the light source is arranged with an axis which is parallelto an axis of the collection lens portion.
 16. A scanning systemaccording to claim 13 wherein the light source is arranged with an axiswhich is substantially parallel +/−5° to an axis of the collection lensportion.
 17. A scanning system according to claim 13 wherein the lightsource is arranged with an axis which is generally parallel to an axisof the collection lens portion.
 18. A scan module comprising a housing;a light source disposed in the housing for generating an optical beamalong an outgoing optical path toward an object to be scanned; adetector for detecting light reflected off the object; a one-pieceplastic molded lens assembly including a collection lens portion and abracket portion, the bracket portion being mounted in the housing andthe collection lens portion collecting the light reflected and/orscattered off the object and focusing it onto the detector; a scanningmirror assembly disposed in the optical path for scanning the opticalbeam for producing at least one scan line toward the object and forreflecting light reflected and/or scattered off the object toward thecollection lens portion.
 19. A scan module according to claim 18 whereinthe collection lens comprises a notch in one side thereof, and whereinthe light source comprises a laser diode module disposed in the notch.